======================================================
WARNING: possible circular locking dependency detected
6.16.0-syzkaller #0 Not tainted
------------------------------------------------------
kworker/u8:8/4594 is trying to acquire lock:
ffff88807caf5358 (&disk->open_mutex){+.+.}-{4:4}, at: __del_gendisk+0xf5/0xbd0 block/genhd.c:710

but task is already holding lock:
ffff88807a3cf988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x136/0x1e0 block/genhd.c:822

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&set->update_nr_hwq_lock){++++}-{4:4}:
       down_write+0x92/0x200 kernel/locking/rwsem.c:1577
       blk_mq_update_nr_hw_queues+0x32/0xcb0 block/blk-mq.c:5041
       nbd_start_device+0x172/0xcd0 drivers/block/nbd.c:1476
       nbd_start_device_ioctl drivers/block/nbd.c:1527 [inline]
       __nbd_ioctl drivers/block/nbd.c:1602 [inline]
       nbd_ioctl+0x219/0xda0 drivers/block/nbd.c:1642
       blkdev_ioctl+0x274/0x6d0 block/ioctl.c:704
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:907 [inline]
       __se_sys_ioctl fs/ioctl.c:893 [inline]
       __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:893
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&nbd->config_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       refcount_dec_and_mutex_lock+0x51/0xc0 lib/refcount.c:118
       nbd_config_put+0x31/0x750 drivers/block/nbd.c:1423
       nbd_release+0xb7/0x190 drivers/block/nbd.c:1735
       blkdev_put_whole+0xb0/0xf0 block/bdev.c:721
       bdev_release+0x47e/0x6d0 block/bdev.c:1144
       blkdev_release+0x15/0x20 block/fops.c:684
       __fput+0x3ff/0xb70 fs/file_table.c:465
       fput_close_sync+0x118/0x260 fs/file_table.c:570
       __do_sys_close fs/open.c:1589 [inline]
       __se_sys_close fs/open.c:1574 [inline]
       __x64_sys_close+0x8b/0x120 fs/open.c:1574
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&disk->open_mutex){+.+.}-{4:4}:
       check_prev_add kernel/locking/lockdep.c:3168 [inline]
       check_prevs_add kernel/locking/lockdep.c:3287 [inline]
       validate_chain kernel/locking/lockdep.c:3911 [inline]
       __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
       lock_acquire kernel/locking/lockdep.c:5871 [inline]
       lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
       __mutex_lock_common kernel/locking/mutex.c:602 [inline]
       __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
       __del_gendisk+0xf5/0xbd0 block/genhd.c:710
       del_gendisk+0x13e/0x1e0 block/genhd.c:823
       nbd_dev_remove+0x3b/0xe0 drivers/block/nbd.c:268
       process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
       process_scheduled_works kernel/workqueue.c:3321 [inline]
       worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
       kthread+0x3c2/0x780 kernel/kthread.c:464
       ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

other info that might help us debug this:

Chain exists of:
  &disk->open_mutex --> &nbd->config_lock --> &set->update_nr_hwq_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  rlock(&set->update_nr_hwq_lock);
                               lock(&nbd->config_lock);
                               lock(&set->update_nr_hwq_lock);
  lock(&disk->open_mutex);

 *** DEADLOCK ***

3 locks held by kworker/u8:8/4594:
 #0: ffff888026956948 ((wq_completion)nbd-del){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3213
 #1: ffffc9000e767d10 ((work_completion)(&nbd->remove_work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3214
 #2: ffff88807a3cf988 (&set->update_nr_hwq_lock){++++}-{4:4}, at: del_gendisk+0x136/0x1e0 block/genhd.c:822

stack backtrace:
CPU: 0 UID: 0 PID: 4594 Comm: kworker/u8:8 Not tainted 6.16.0-syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: nbd-del nbd_dev_remove_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_circular_bug+0x275/0x350 kernel/locking/lockdep.c:2046
 check_noncircular+0x14c/0x170 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3168 [inline]
 check_prevs_add kernel/locking/lockdep.c:3287 [inline]
 validate_chain kernel/locking/lockdep.c:3911 [inline]
 __lock_acquire+0x126f/0x1c90 kernel/locking/lockdep.c:5240
 lock_acquire kernel/locking/lockdep.c:5871 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5828
 __mutex_lock_common kernel/locking/mutex.c:602 [inline]
 __mutex_lock+0x199/0xb90 kernel/locking/mutex.c:747
 __del_gendisk+0xf5/0xbd0 block/genhd.c:710
 del_gendisk+0x13e/0x1e0 block/genhd.c:823
 nbd_dev_remove+0x3b/0xe0 drivers/block/nbd.c:268
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238
 process_scheduled_works kernel/workqueue.c:3321 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3402
 kthread+0x3c2/0x780 kernel/kthread.c:464
 ret_from_fork+0x5d4/0x6f0 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>